Air filtering assemblies are known that can be used to remove particles from air in an enclosed space. Typically such air filtering assemblies include an air filter which can include a sheet of air filtering material or can work by electrostatic attraction, and also include a fan assembly that moves the air through the air filter. Such air filtering assemblies can continuously circulate a small portion of the air in the enclosed space through the filter so that over time the air filtering assembly improves the cleanliness of the air in the enclosed space. U.S. Pat. Nos. 4,477,272, 4,781,526, 6,045,329, and 6,264,727 describe such air filtering assemblies.
U.S. Pat. No. 4,781,526 describes such an air filtering assembly that is a combination of (1) a portable box fan assembly having a parallelepiped housing with square open sides on which protective grills are mounted, an electric motor having a fixed portion mounted on and within the housing and a rotor assembly on which is mounted a fan also within the housing that, when the motor is activated via means for connecting the motor to a source of electric power included in the box fan assembly, rotates about an axis normal to and generally centered on the side surfaces to move air through the protective grills, and (2) a filter assembly including a parallelepiped frame having opposite rectangular sides with through openings generally corresponding in size to the open sides of the housing of the box fan assembly and including a peripheral wall between the peripheries of the sides, and a sheet of air filtering material within the filter assembly frame between its sides. The air filtering assembly described in both U.S. Pat. No. 4,781,526 has special structure 16 included with the housing for positioning and retaining the filter assembly with one of its sides along and aligned with one of the side surfaces of the box fan. Thus, it would be difficult for a person who had filter assembly of the type described above and a box fan assembly of the type described above without that special structure to position and retain the filter assembly with one of its sides along and aligned with one of the side surfaces of the box fan assembly to make an air filtering assembly.